The present invention relates generally to the field of laser beam scanning systems, and more particularly to micro-electro-mechanical systems (MEMS) for laser beam scanning. Miniature laser beam scanning systems are important for applications such as barcode scanning, machine vision and, most importantly, xerographic printing. The use of MEMS to replace standard raster output scanning (ROS) in xerographic print engines allows simplification of printing systems by eliminating macroscopic mechanical components and replacing them with large arrays of scanning elements. Advanced computation and control algorithms are used in managing the large arrays of scanning elements.
Such MEMS based printing systems are entirely solid state, reducing complexity, and allowing increased functionality, including compensation of errors or failures in the scanner elements. An important step in constructing solid state scanning systems is integrating the semiconductor light emitter directly with MEMS actuators to gain the desired optical system simplification. Integrated scanners, which have lasers and scanning mirrors in the same structure, have been demonstrated using manual placement of laser chips onto MEMS wafers with micromachined alignment parts and adhesives by L. Y. Lin et al in Applied Physics Letters, 66, p. 2946, 1995 and by M. J. Daneman et al in Photonics Technology Letters, 8(3), p. 396, 1996. However, current techniques do not allow wafer-scale integration of the light-emitter and MEMS device.
In accordance with the present invention a laser beam scanner consisting of a single crystal silicon (SCS) deflection and scanning mirror is integrated with a laser diode or light emitting diode. By combining methods of deep reactive ion etching (deep RIE) of silicon with solder bump bonding methods, completed and tested laser diodes are integrated with silicon (Si) or silicon on insulator (SOI) substrates supporting MEMS layers. Details of creating a torsional mirror and actuating it magnetically or electrostatically are detailed in U.S. Pat. No. 5,629,790 by Neukermans and Slater which is incorporated herein by reference in its entirety.
Using solder bump bonding methods, completed and tested laser diodes are bonded to silicon MEMS built using a typical surface and bulk micromachining processes. Because of the deep RIE recesses, the laser diode solder bumps can be passively aligned to those on the host substrate. In addition, the deep RIE recesses allow nearly coplanar laser chip and Si surfaces to be made. The use of the SCS layer of an SOI wafer, rather than the polysilicon film provides for the introduction of very flat and smooth mirrors and high reliability torsion bars. The device is easily scalable to arrays of lasers and scanning mirrors on a single wafer.
Integration of the scanner and light source eliminates the need for external, manual positioning of light sources and scanning mirrors. Simplified and more cost effective post-processing steps such as interconnect metallization can be realized because the use of an etched recess results in nearly planar surfaces. In addition, pick and place technologies commonly used for multi-chip module assembly can be adapted for wafer scale assembly and bonding of light sources to the carrier substrate. With such commercial systems, bare die can be placed with accuracy better than .+-.30 .mu.m.
Thus, the present invention allows the integration of completed and tested light emitting devices directly with the MEMS actuators to gain the desired simplification of the optical system needed to realize solid state scanning systems.